Composition to be used in the resin injection molding technique, containing low molecular weight compounds jointly forming a hybrid network

ABSTRACT

The present invention relates to a reaction injection molding process, to a composition utilized therein as well as to a kit of parts from which the composition can be obtained. In particular, the process includes the use of a composition which contains at least 70% of low molecular weight compounds which are capable of forming a crosslinked polymer. The first component of the composition is a compound with at least an ethylenic unsaturation and an isocyanate-reactive group. The second component of the composition contains an ethylenically unsaturated monomer capable of copolymerizing with the first component. The third component of the composition is a polyisocyanate. Polymerization of the first and second components takes places prior to the reaction between the first and third components.

This is a continuation of Application No. 07/949,858, filed on Nov. 20,1992 which was abandoned upon the filing hereof.

The invention relates to a composition to be used in the Resin InjectionMoulding technique, which composition substantially contains lowmolecular weight compounds capable of forming a hybrid network, whichcomposition at least contains a first component consisting of a compoundwith at least an ethylenic unsaturation and an isocyanate-reactivegroup, and a second component containing an ethylenically unsaturatedmonomer capable of copolymerizing with the first component, and a thirdcomponent, which is a polyisocyanate.

Such a composition is described in U.S. Pat. No. 4,822,849. In it thefirst component is an unsaturated polyester with terminal hydroxylgroups. Such a composition has been found to have the disadvantage thatit shrinks during the curing. U.S. Pat. No. 4,822,849 provides asolution for it by reducing the number of unsaturations in theprepolymer, so that the shrinkage resulting from the radicalpolymerization is reduced. However, the disadvantage of this measure isthat the mechanical properties of the material deteriorate inconsequence of the reduction of the crosslink density. At the same time,the viscosity of the composition is rather high. In certain applicationsthis is a disadvantage.

The object of the invention is to provide a low viscosity compositionwith which products with good mechanical properties may be obtained.

An other object of the invention is to provide a low viscositycomposition with which products may be obtained with little or nopolymerisation shrinkage.

This is achieved according to the invention in that the composition is acomposition of monomers with a molecular weight lower than 1000, thefirst component of which substantially consists of a monomer withsubstantially 1 terminal vinyl group per molecule and furthersubstantially 1 isocyanate-reactive group per molecule and has amolecular weight lower than 500.

From DE-A-2,209,149 a composition is known containing, inter alia, anethylenically unsaturated monomer and an adduct of a polyisocyanate anda monomer with an isocyanate-reactive group and a terminal vinyl group,but in it, before mixing the adduct with the ethylenically unsaturatedmonomer, the polyisocyanate is first prepolymerized, at least in part,with a polyol and with the monomer with the isocyanate-reactive groupand the terminal vinyl group. This composition does not exhibit a lowviscosity. With the known composition a reduction of the polymerisationshrinkage according the invention is not possible. DE-A-2,209,149 doesnot mention that this composition can be used for the Resin InjectionMoulding (RIM) technique.

From U.S. Pat. No. 3,856,830 a composition is known containing apolyisocyanate and also a monomer with an isocyanate-reactive group anda terminal vinyl group. The polyisocyanate reacts with this monomer toform a urethane oligomer with terminal unsaturations which is capable ofpolymerizing, optionally in the presence of an ethylenically unsaturatedmonomer. So, in U.S. Pat. No. 3,856,830, there will first be a reactionof the polyisocyanate with the monomer with the unsaturation and withthe isocyanate-reactive group and only after that a composition isobtained of the reaction product with an ethylenically unsaturatedmonomer.

This composition does not exhibit a low viscosity. With the knowncomposition a reduction of the polymerisation shrinkage according theinvention is not possible.

U.S. Pat. No. 3,856,830 does not mentioned that the composition can beused for the RIM technique.

From EP-A-197682 a polymerisable composition is known comprising anethylenically unsaturated monomer, a low profile additive and an adductof a polyisocyanate and a monomer with an isocyanate reactive group anda terminal vinyl group. The polyisocyanate is always completelyconverted into an unsaturated urethane monomer. The low profile additiveis an organic polymer. The know polymerisable composition has thedisadvantages that first an unsaturated urethane monomer has to besynthesized and that the low profile additive has to be solved into thecomposition before an in-mould reaction can take place. The knowncomposition does not exhibit a low viscosity due to the general factthat dissolving a polymer rises the viscosity of the solvent. Further,with the known composition a reduction of the polymerisation shrinkageaccording the invention is not possible.

From EP-A-0064809 a method of producing moulded plastic products byin-mould polymerisation, of an unsaturated urethane component and avinyl monomer copolymerisable therewith, is known. The unsaturatedurethane component is derived from a hydroxyalkyl acrylate ormethacrylate by reaction of hydroxyl groups thereof with the isocyanategroups of a polyisocyanate free from urethane groups or with theisocyanate groups of an urethane polyisocyanate. The known in-mouldreaction can not be performed according a procedure according thepresent invention i.e. first initiating the radical polymerisationbetween the ethylenically unsaturated monomers and subsequently causingthe crosslinking to take place by reacting the isocyanates with theisocyanate-reactive groups.

Hence, none of the four references DE-A-2,209,149, U.S. Pat. No.3,856,830, EP-A-197682, EP-A-64809, describes a system in which both aradical polymerisation and a urethane forming reaction takes place inthe mould, since none of the references has free isocyanate in itseventual reaction mixture.

The composition according to the invention preferably consists ofmonomers with a molecular weight lower than 500, and the first componentsubstantially consists of monomers with a molecular weight lower than400.

The isocyanate-reactive group is preferably a hydroxyl group.

A composition substantially containing low molecular weight compounds isunderstood to mean within the scope of this invention a compositioncontaining at least 70% (wt) of such compounds.

An example of the first component is the hydroxyl ester of acrylic acidor methacrylic acid or an allyl alcohol or alkoxylated allyl alcohol.

Using the RIM technique, it has proved to be possible, with thecomposition according to the invention, to obtain articles with goodmechanical and good thermal properties. The HDT in particular is higherthan would have been expected by a person skilled in the art.

The first component preferably has the following general formula:##STR1## where R is a hydrogen or methyl R¹ is an alkylene group with 2or 3 carbon atoms and n is a whole number between 1 and 6.

These materials can be made by reacting acrylic acid or methacrylic acidwith an alkylene oxide, chosen from the group consisting of ethyleneoxide and propylene oxide, in a manner generally known in the art. Thenumber n in the formula equals the ratio between the number of alkyleneoxide moles and the number of acrylic acid or methacrylic acid moles.

Examples of the first component are, inter alia, hydroxylpropylmethacrylate, hydroxylethyl methacrylate, hydroxylethyl acrylate,hydroxypropyl acrylate, polyoxyethylene(2)acrylate,polyoxyethylene(2)methacrylate, polyoxyethylene(3)acrylate,polyoxyethylene(3)methacrylate,polyoxypropylene(2)acrylate,polyoxypropylene(2)methacrylate,polyoxypropylene(3)acrylate and polyoxypropylene(3)methacrylate.

A composition according to the invention makes it possible for a systemto be cured by first subjecting the ethylenic unsaturations in the firstcomponent together with the ethylenically unsaturated monomers of thesecond component to a radical polymerization process and subsequentlycausing the crosslinking to take place by reacting the isocyanates withthe isocyanate-reactive groups of the first component.

Preference is given to first initiating the radical polymerization. Inradical polymerization there will be some degree of shrinkage. As thenumber of unsaturations per molecule of the first and of the secondcomponent equals 1, the radical copolymerization will result in theformation of a linear polymer. As the polymer is linear, andconsequently thermoplastic, it is possible to meter an amount of resincomposition to the mould afterwards to compensate for the shrinkage.After that, the curing is effected via the polyisocyanates, during whichcuring process, however, the shrinkage is substantially less than duringthe preceding radical polymerization. During the formation of theurethane, the crosslinking takes place. The succession of the variousreactions can be pre-set by the choice of the reaction conditions and ofthe various catalysts, according to techniques known in the art.

Besides, it is possible to cause the radical and urethane reactions totake place simultaneously in order to obtain a quick total reaction. Itis further possible to allow the radical reaction to take place afterthe urethane reaction. This is e.g. described in EP-A-197.682, examples1-5 page 10, but then it will no longer be possible for the amount ofshrinkage that occurs during the radical step in the curing process tobe reduced by subsequent metering of material.

The advantage of a composition according to the invention is that thenon-reacted composition only contains low molecular weight componentsand therefore has a low viscosity. A composition according to theinvention generally has a viscosity of between 1 and 150 mPas measuredat 23° C. on a composition containing the first and second components inan arbitrary weight ratio, for instance 1:1.

This is a major advantage when used in processing techniques like thesaid resin injection moulding technique (RIM technique).

It is an other advantage of the composition according to the inventionthat articles can be made with it in a mould using the RIM technique, inwhich process the shrinkage that occurs is compensated by subsequentmetering of material, which makes it possible, inter alia, to producearticles with a smooth surface structure and a good dimensionalstability.

The invention also relates to a process for using a composition asdescribed hereinbefore in resin transfer moulding (RTM), reactioninjection moulding (RIM), reinforced reaction injection moulding (RRIM)and preferably in structural reaction injection moulding (SRIM).

RIM is a technique in which a mixture is injected into a mould and afterinjection cures within a short period of time.

RRIM is a RIM technique in which the mixture also contains fibrousreinforcing material.

SRIM is a RIM technique in which a fibrous reinforcing material isalready contained in the mould before the injection of the mixture.

It is possible for the said mixtures to be prepared immediately beforeinjection by mixing two or more submixtures which are not reactiveindividually, but do provide a reactive mixture when combined.

RTM is a technique to be regarded as equivalent to SRIM in which anamount of fibrous material is contained in a mould and a mixture isinjected into the mould. Optionally, a vacuum can be created in themould. RTM differs from SRIM in that the mixture is usually not preparedby mixing two or more submixtures just before injection.

In the SRIM technique in particular it is an advantage for the mixtureto be of a low viscosity, because in the SRIM technique the wetting ofthe fibres must be take place in the mould within a short period oftime.

So the composition may contain fibrous reinforcements to improve themechanical properties of the articles prepared from the composition.Generally, 5 to 80% (wt) fibrous material can be added.

Suitable fibrous materials are glass, asbestos, carbon and organicfibrous materials, such as aromatic polyamides. Glass fibres may bepresent in any suitable form, for instance in the form of a mat, tape orribbon, in the form of continuous fibres or chopped staple fibres. Inthe form of continuous fibres they may have a random structure, or mayhave been processed to form a fabric.

When using the composition, it is possible for the fibrous reinforcementto be added to the mixture to be injected (RRIM), provided these fibresare short enough, and it is possible also for the fibrous structure tobe put in the mould before the injection (SRIM).

If processed in a process according to the invention, the compositionaccording to the invention has the advantage that the composition atfirst consists of a mixture of low molecular weight monomers having alow viscosity. This makes it possible for the mixture to be injectedinto a mould already containing fibrous reinforcing material, in which aproper wetting of the fibrous material can take place. Depending on thechoice of the curing system, the radical curing can now be carried outfirst and the urethane curing afterwards, or the urethane curing processcan be carried out first and the radical curing afterwards, or the twocuring processes can be carried out virtually simultaneously.

Preferred is the curing system in which the radical curing is carriedout first followed by the urethane curing.

The unsaturated monomer which the second component consists of can bechosen from all monomers capable of reacting with the ethylenicUnsaturation of the first component, including vinyl monomers such as,for instance, vinyl esters, vinyl ethers, aromatic vinyl compounds,vinyl nitriles, acrylates or methacrylates. Examples are styrene,α-methylstyrene, p-methyl-styrene, vinyl toluene and methyl, ethyl,propyl acrylate or methacrylate. Suitable also are monomer mixtures. Itis possible also to use bifunctional or multifunctional monomers, suchas divinyl benzene, diailyl phthalate or triallyl cyanurate. The lattermonomers are preferably applied in relatively small amounts.

The ratio of the second component and the first component is between95:5 and 5:95 (in weight). Preferably the ratio is between 80:20 and20:80. The choice is determined by, among other things, the desiredcrosslink density of the cured composition.

The third component contains at least an average of more than 1.75isocyanate groups, and preferably 2 to 3 isocyanate groups per molecule.More preferably the functionality is 2.2 to 2.7 on average. Thepolyisocyanate may, for instance, be an aliphatic, an aromatic or acycloaliphatic polyisocyanate, or a combination of two or more differentgrades. Examples are toluene diisocyanates. 1,5-naphthalenediisocyanate, cumene-2,4-diisocyanate, 4-methoxy-1,3-phenylenediisocyanate, 4-chloro-1,3-phenylene diisocyanate, 4-bromo-1,3-phenylenediisocyanate, 4-ethoxy-1,3-phenylene diisocyanate, 2,4'-diisocyanatodiphenylether, 5,6-dimethyl-1,3-phenylene diisocyanate,2,4-dimethyl-1,3-phenylene diisocyanate, 4,4'-diisocyanate diphenylether benzidine diisocyanate, 4,6-dimethyl-13-phenylene diisocyanate,durene diisocyanate, 4,4'-diisocyanate dibenzyl,3,3'-dimethyl-4,4'-diisocyanate diphenyl, 2,4-diisocyanate stilbene,3,3'-dimethoxy-4,4'-diisocyanate phenyl methane,3,3'-dimethoxy-4,4'-diisocyanate diphenyl, 1,4-anthracene diisocyanate,2,5-fluorene diisocyanate, 1,8-naphthalene diisocyanate,2,6-diisocyanato benzfuran amyl benzene-2,4diisocynate, hexylbenzene-2,4-diisocyanate, dodecyl benzene-2,4-diisocyanate, butylbenzene-2,4-diisocyanate.

The polyisocyanate is preferably carbodiimide-modified diphenylmethane4,4'-diisocyanate.

It is possible to influence the degree of cross-linking by addingmono-functional isocyanates or mono-alcohols or mono-amines withoutethylenic unsaturation. It is possible also to vary the number ofcrosslinkages of each amount of composition by adding as a fourthcomponent a diol, polyol or other polyfunctional isocyanate-reactivecomponent, such as diamines or amino alcohols, and optionally also anexcess of polyisocyanate, so that longer polyurethane lengths will beformed between the crosslinks.

Preference is given to the addition of 2-20% (wt), calculated on thetotal composition, of a fourth component with two or moreisocyanate-reactive groups or two or more ethylenic unsaturations and amolecular weight of 500 to 3000.

Generally, the number of isocyanate groups calculated on the number ofhydroxyl groups (NCO/OH)is not fewer than 0.8 and not more than 1.6(mole/mole). It is possible to add a higher ratio of isocyanate groups,but then the mechanical properties of articles made from the compositionwill deteriorate.

The mixture contains catalysts promoting the copolymerization of theunsaturated monomer in the second component with the unsaturation in thefirst component. These may in principle be the same systems as used inthe case of unsaturated polyesters, when used as RIM system, theformation of gas is undesirable and that is why moisture-containingperoxide catalysts are less desirable. Examples of radical-formingsubstances are peroxides, such as hydroperoxides, ketone peroxides andperesters. Examples are benzoyl peroxide, ditertiary butyl peroxide,cyclohexanone peroxide, tertiary butyl perbenzoate and tertiary butylperoctoate, as well as photoinitiators sensitive to visible light orultraviolet-sensitive photoinitiators.

The amount of catalyst is usually between 0.5 and 5% (wt) calculated onthe unsaturated components. Besides, an accelerator may be present, forinstance a cobalt compound or an amine.

The composition may further contain catalysts for the urethane reaction.If both catalyst systems are used, the gellation may be very rapid, sothat in the production process short cycle times can be realized.

Compositions like those of the invention have a low viscosity and cantherefore be easily moulded or injected. It is possible in the processto fill the composition with fillers, fibre reinforcements and the likewithout such an increase of the viscosity that the composition can nolonger be used in the RIM process.

The composition may also contain additions like pigments, stabilizers,for instance antioxidants and UV stabilizers, fillers like talc, mica,calcium carbonate, aluminium or carbon black.

Compositions according to the invention can be used, inter alia, for theproduction of articles according to the RIM technique. The compositionwill generally be used in a so-called binary system (two-componentsystem) which consists of a first binary system consisting of a firstelement containing a first component consisting of a compound with atleast an ethylenic unsaturation and an isocyanate-reactive group andoptionally an amount of a second component containing an unsaturatedmonomer capable of polymerizing with the first component, and a secondelement containing a third component, which is a polyisocyanate, andoptionally an amount of the second component, characterized in that thefirst component substantially consists of the hydroxyl ester of(meth)acrylic acid. The catalysts and/or initiators are distributed overthese elements according to a process known to the person skilled in theart.

The invention will be elucidated by means of the following exampleswithout being limited thereto.

The mechanical properties were determined as follows: tensile strength,elongation at break and E modulus according to DIN 53455, flexuralstrength and E modulus according to DIN 53452, impact strength accordingto to DIN 53453, HDT according to ASTM-D-648-72 and Barcol hardnessaccording to ASTM-D2583. The acid number was determined according to DIN53402. The hydroxyl number was determined according to DIN 53240. Theviscosity was determined with a Brookfield viscometer, type HBTD, withspindle 1,100 rpm.

EXAMPLE I

To a mixture of 200 g hydroxyethyl methacrylate (HEMA) and 200 g styrenewas added 8 g benzoyl peroxide (BPO) (50% paste) as radical initiator,and dissolved.

After that the mixture was deaerated. Subsequently were added 0.8 gdiethyl aniline (DEA) as accelerator, 220 g carbodiimide-modifiedmethylene-4,4'-diphenyl-diisocyanate (MDI) with a functionality of 2.3(IsonateR 143 L of Dow Chemicals) and 0.01 g dibutyltin diacetate asurethane catalyst. The viscosity of the mixture was 15 mPa.s at 23° C.The mixture was poured between two flat chromium-plated sheets (20×40mm) that were 4 mm apart. The product of example 1 was subjected to thefollowing curing cycle: 20 hours 25° C., 4 hours 40° C., 4 hours 80° C.and 8 hours 120° C. Subsequently, test bars were sawn. On these bars themechanical properties and HDT were determined. They are mentioned intable 1.

The product is characterized by excellent mechanical properties (highstrengths and moduli) and a good HDT. By extra aftercuring for 4 hoursat 200° C. the HDT is even increased to 165° C. without adverselyaffecting the mechanical properties.

                  TABLE 1                                                         ______________________________________                                        Mechanical properties                                                         Example          I       II      III   IV                                     ______________________________________                                        HDT (°C.) 142     129     116   148                                    Tensile strength (MPa)                                                                         108     96      91    94                                     E-modulus (GPa) (DIN 53455)                                                                    4100    3390    3500  3420                                   Elongation at break (%)                                                                        4.6     4.2     7.1   4.0                                    Flexural strength (MPa)                                                                        164     155     157   141                                    E-modulus (GPa) (DIN 53452)                                                                    3680    3500    3450  3380                                   Impact strength (kJ/m2)                                                                         15     16      30    16                                     Barcol hardness   40     40      42    44                                     ______________________________________                                    

EXAMPLE II

The process of example I was repeated using 100 g HEMA, 300 g styreneand 110 g MDI. The viscosity of the mixture was 10 mPa.s. The mechanicalproperties are shown also in table 1.

EXAMPLE III

The process of example I was repeated using a mixture consisting of 100g HEMA, 260 g styrene and 40 g ethoxylated bisphenol A (BPA.12EO), which124 g MDI was added to.

The viscosity of the resulting composition was 14 mPa.s at 23° C.

The aftercuring cycle was 20 hours at 25° C., 4 hours 40° C., 4 hours80° C., 4 hours 120° C. and 4 hours 160° C. The mechanical propertiesare shown in table 1.

It has been found that by adding a long-chain diol the impact strengthof the product can be increased without the HDT being lowered too much.

EXAMPLE IV

The process of example I was repeated using a mixture consisting of 100g HEMA, 243 styrene and 57 g vinyl ester (the reaction product of thediglycidyl ether of bisphenol A with 2 moles methacrylic acid), which133 g MDI was added to. The viscosity of the resulting composition was13 mPa.s at 23° C.

The aftercuring cycle was 20 hours at 25° C., 4 hours 40° C., 4 hours80° C., 4 hours 120° C. and 4 hours 160° C. The mechanical propertiesare shown in table 1.

This composition, too, gives excellent mechanical properties and a highHDT.

EXAMPLES V AND VI

The volume shrinkage of examples I, II, III and IV was 8%.

The volume shrinkage of the composition of Example I and Example II werereduced to 3% (Ex. V) and 2% (Ex. VI) respectively by applying thepolymerisable composition according the invention in a RIM-apparatus. Insuch apparatus the polymerisable composition was kept under pressureduring curing. Due to the fact that first the radical polymerisationtook place, resulting in a thermoplastic polymer, the volume shrinkagewas compensated by the addition of material which was pressed into themould, after which further curing took place.

I claim:
 1. A reaction injection molding process for making productsfrom a composition which contains at least 70% of low molecular weightcompounds capable of forming a crosslinked polymer, which compositioncontains a first component consisting of a compound with at least anethylenic unsaturation and an isocyanate-reactive group, a secondcomponent containing an ethylenically unsaturated monomer capable ofcopolymerizing with the first component, and, as a third component, apolyisocyanate, wherein the first, second and third components aremonomers having a molecular weight less than 1000, the first componentconsists of a monomer having 1 terminal vinyl group and 1isocyanate-reactive group per molecule and a molecular weight less than500, wherein the polymerization of the first and second components takesplace before the reaction of the first and third components.
 2. Processaccording to claim 1, characterized in that the composition alsocontains 2 to 20% of a fourth component, which component has two or moreisocyanate-reactive groups or two or more ethylenic unsaturations and amolecular weight of between 500 and
 3000. 3. Process according to claim1, characterized in that the composition consists of monomers with amolecular weight lower than 500, the first component of which consistsof monomers with a molecular weight lower than
 400. 4. Process accordingto claim 1, characterized in that the isocyanate-reactive group is ahydroxyl group.
 5. Process according to claim 1, characterized in thatthe first component has the following general formula: ##STR2## where Ris a hydrogen or methyl, R¹ is an alkylene group with 2 or 3 carbonatoms and n is a whole number between 1 and
 6. 6. Process according toclaim 1, characterized in that the ratio of the second component and thefirst component is between 95:5 and 5:95 (in weight).
 7. Processaccording to claim 1, characterized in that the third component containsat least an average of 1.7 isocyanate groups.
 8. Process according toclaim 1, characterized in that the third component contains an averageof 2.2 to 2.7 isocyanate groups.
 9. Process according to claim 1,characterized in that the second component is chosen from the groupconsisting of styrene, p-methylstyrene, vinyl toluene, methyl-, ethyl-,propyl acrylate or methacrylate.
 10. Process according to claim 1,characterized in that the composition has a viscosity of between 1 and150 mPa.s measured at 23° C.
 11. Process according to claim 1 whereinthe first component consists of at least 70% of the hydroxylester of(meth)acrylic acid.
 12. Product obtainable by the process according toclaim
 1. 13. Composition to be used in Resin Injection Molding technique(RIM) which contains at least 70% of low molecular weight compoundscapable of forming a crosslinked polymer, which composition contains atleast a first component which consist of a compound with at least anethylenic unsaturation and an isocyanatereactive group and which has 1terminal vinyl group and 1 isocyanate-reactive group per molecule, asecond component containing an ethylenically unsaturated monomer capableof copolymerizing with the first component, a third component which is apolyisocyanate, and 2-20% of a fourth component containing at least anisocyanate reactive group or an ethylenic unsaturation, wherein thefirst, second and third components are monomers having a molecularweight less than 1000, the first component having a molecular weightlower than 500, the fourth component of which has two or moreisocyanate-reactive groups or two or more ethylenic unsaturations and amolecular weight between 500 and 3000, wherein the polymerization of thefirst and second components takes place before the reaction of the firstand third components.
 14. Kit of parts consisting essentially of a firstelement and a second element, said first element containing a compoundwith at least an ethylenic unsaturation and an isocyanate-reactivegroup, and said second element containing a polyisocyanate, wherein atleast about 70% of said first component is the hydroxyl ester of(meth)acrylic acid.
 15. Kit of parts according to claim 14, whichconsists essentially of said first element and said secondelement,wherein said compound contained in said first element comprisesa first component and is represented by the following general formula:##STR3## where R is a hydrogen or methyl, R¹ is an alkylene group with 2or 3 carbon atoms and n is a whole number between 1 and 6, and with amolecular weight lower than 500; wherein said polyisocyanate of saidsecond element comprises a third component and has a molecular weightless than 1000; wherein said first element or said second elementcontains a radical catalyst; wherein at least said first element or saidsecond element contains a second component which is a monomer having oneethylenic unsaturation and having a molecular weight below 1000; andwherein the weight ratio of the second component to the first componentis between 95:5 and 5.95.